With mostly IAPs, you might also consider looking into Central. I suggest striking up a conversation with the sales team to see what they suggest for such a deployment.
With AirWave, those numbers seem about right. You can also inquire to the sales team about the future AirWave scale solution (it's going by a few different names, but I still refer to it as AirWave 10) - if it's release lines up with your deployment timeline, it could also be a viable option.